SplintER Series: A Rare Cause of Traumatic Thumb Pain

• Dislocation of the first carpometacarpal (CMC) joint.
• Pearl: CMC dislocations account for less than 1% of all hand injuries [1,2]. Isolated dislocations are even more uncommon, and are usually associated with Bennett, Rolando, and carpal fractures [1-4]. The majority of dislocations are dorsal [2,4]. Misdiagnosis or delayed treatment may result in joint instability, early degeneration of the articular cartilage, and decreased grip strength [1-5].
• Bonus: There are two other interesting findings on this radiograph. First, there is a well corticated osseous fragment at the base of the second proximal phalanx that is likely a chronic fracture deformity. Second, there is a metallic foreign body between the third and fourth metacarpal heads that is possibly a BB gun pellet.

• Thumb CMC dislocations are often caused by axial loading of the thumb in a flexed position, and less commonly, direct force into the webspace between the first and second digits [1-4].

• Exam findings include painful and limited range of motion of the thumb and often subtle deformity and swelling over the dorsoradial side of the hand [1,4].

• Plain radiographs should be taken of the hand with AP, lateral, and oblique views [1-3]. Stress views and CT scan may also be helpful to identify other injuries, as thumb CMC dislocations are rarely isolated [1,2].

• The CMC dislocation should be anesthetized with an intra-articular injection, and then closed reduction should be performed with traction [1,4].
• Immobilize the joint with a thumb spica splint with the first metacarpal held in abduction and extension with the wrist in pronation. Closed reduction is often unstable [1-6].
• The patient should have follow-up arranged with a Hand Specialist within 3-4 days [1,7]. 

Figure 2. Post-reduction XR that showed interval reduction of the first CMC joint with normal alignment. Author’s own images.

• Orthopedics should be immediately consulted for a thumb CMC dislocation if there is an open fracture-dislocation, neurovascular compromise, or irreducible dislocation.

• There is debate over the optimal treatment strategy, and several studies have compared nonoperative and operative treatment [4].
• Nonoperative management: immobilization in a short arm thumb spica cast for 4-6 weeks [2].
• Operative treatment: closed reduction and percutaneous fixation with Kirschner wires for 5-6 weeks [3-7].
• Patients who experience persistent instability may require ligamentous reconstruction [3-5].